The present invention relates to a vehicle headlamp constructed to switch beams by moving a movable shade.
A vehicle headlamp is constructed such that a beam for low beam or high beam is emitted by reflecting forward light from a light source with a reflector. Since light distribution patterns required for the low beam and the high beams are different, in general, two light sources are selectively switched on or off such that the headlamp switches between the low beam and the high beam.
However, there are vehicle headlamps constructed to switch beams using a single light source. In particular, such construction is found with many two-unit type headlamps, which have a discharge bulb as a light source bulb.
One conventional beam switching method that uses a single light source switches beams with a movable shade. In this method, the shade is designed to move between two positions each providing a different degree of screening of incident light given off from a light source to a reflector with a beam switching device comprising an actuator such as a solenoid.
When the movement of the shade is performed through a rotational motion, the shade is constructed to rotate about a rotational axis extending horizontally by the beam switching device disposed below the light source.
However, if the shade is constructed to rotate about the rotational axis extending horizontally, its vertical dimension from the light source to a lower end of the beam switching device must be increased. Because of this, for a lamp in which the vertical width of a reflector below a light source of the lamp is narrow and the lower end portion of the beam switching device protrudes below the reflector, the lamp would have to be made large to contain the protruding portion.
The present invention was made in view of these situations. An object thereof is to provide a vehicle headlamp constructed such that beams are switched by rotating a shade. A beam switching device can be incorporated in the headlamp without unnecessarily making the headlamp large.
The present invention attains the above object by devising the orientation of a rationale axis for the shade.
According to an embodiment of the invention, there is provided a vehicle headlamp comprising a light source, a reflector for reflecting forward light from the light source, a shade for screening part of incident light given off from the light source to the reflector and a beam switching device for switching between a low beam and a high beam by rotating the shade between two positions providing respectively a different degree of screening of the incident light by the shade. The beam switching device is constructed so as to rotate the shade about a rotational axis extending in a direction that is inclined at a predetermined angle relative to a horizontal plane.
The kind of the above xe2x80x9clight sourcexe2x80x9d is not limited to any specific one, but may be a discharge illuminant portion of a discharge bulb or a filament of an incandescent bulb such as a halogen bulb.
The xe2x80x9cshadexe2x80x9d may be a shade of any type and no specific construction is required therefor, provided that the shade can screen part of incident light given off from the light source to the reflector.
There is no specific limitation imposed on the xe2x80x9cpredetermined angle.xe2x80x9d However, if this is set to a large value, the vertical dimension from the light source to the lower end position of the beam switching device can be made shorter. If the angle is set to a value too large, the shade and a rotating mechanism portion of the beam switching device may interfere with a reflecting surface area of the reflector to adversely affect the light distribution of the lamp. Therefore, the xe2x80x9cpredetermined anglexe2x80x9d may be set to a suitable value that achieves a good balance between those two factors.
As shown in the foregoing construction, the Vehicle headlamp according to the invention comprises the beam switching device for switching between the low beam and the high beam by rotating the shade for screening part of incident light given off from the light source to the reflector between two positions providing respectively a different degree of light screening. The beam switching device is constructed so as to rotate about the rotational axis extending in the direction that is inclined at a predetermined angle relative to the horizontal plane. Consequently, the following function and effectiveness can be obtained.
The rotational locus of the shade can be inclined relative to the vertical plane by inclining the rotational axis of the shade relative to the horizontal plane. Along with this, the beam switching device can also be inclined relative to the vertical plane. Therefore, the vertical dimension from the light source to the lower end position of the beam switching device can be made shorter.
As mentioned previously, there is no specific limitation to the magnitude of the xe2x80x9cpredetermined angle.xe2x80x9d If it is set between 30 to 60 degrees, the vertical distance between the light source to the lower end position of the beam switching device can be made shorter without adversely affecting the light distribution of the lamp.
In general, a non-light incident area on a reflector where light from a light source is not permitted to enter varies as a shade rotates. In a case where a rotational axis of the shade inclines relative to the horizontal plane as in the case of the construction described above, the variation of the non-light incident area differs between reflecting surfaces on left and right sides of the light source. The variation is larger at the reflecting surface on one side (left or right side) than at the reflecting surface on the other side where the rotational axis is disposed.
In the construction described above, when the shade is located at the low beam position and the non-light incident area is set such that this area is larger at one side of the reflecting surface of the light source than at the other side of the reflecting surface where the rotational axis is disposed, not only the non-light incident area can be used as a light incident area when the shade is located at the high beam position but also a rotational angle of the shade required for beam switching can be set to a small value. Thus, the beam switching device can be made compact.
Here, the xe2x80x9clow beam positionxe2x80x9d refers to one of the two positions which provides a larger degree of screening, while the xe2x80x9chigh beam positionxe2x80x9d refers to the other position which provides a smaller degree of screening.